Hi, just to share my experience.

Initial Height & Weight: 166cm & 51-53kg+/-
12 weeks progress result: 57.7-58kg+/-

- Consume proper meal everyday in a timely manner. Every meal should includes protein, calories and min. fats.
ie.Chicken Breast,Milk,Bread,Egg,Fish,Red Meat (not too often),fresh vege & fruits..etc.
- Regular Workout + Protein / Muscle mass gain drink (OPTIONAL)
- Cut down alcohol / nicotine intakes
- Cut all Fast Foods & Junk Foods. It only boost up your FATS!
- SUFFICIENT REST. Sleep at least 6-7 hours per day - IMPORTANT
- Consume alot of WATER.

My regular daily intakes:
Breakfast:
2-3 x Hard boiled eggs or
Chicken salad (with/without salmon or grill fish sometimes)

Tea-break:
Cereal drink
Banana
Soya drink / Milo or any other similar drink

Lunch:
Rice + Meat (Chicken / Beef / Mutton) or
Rice w/ alot of Vege / Fish / Tofu / Egg

Pre-workout (30mins before):
Bread

Post-workout:
Weight Gain/Muscle Gain - Protein Drink + Milk

Dinner:
2 x Chicken Breast or
Rice w/ Fish + alot of Vege

The above recipe is not any professional weight gain guide but solely based on my own experience. Feel free to try it out yourself. Results may vary. It's not hard to gain weight if you have discipline in your food intake. Determination is what counts.

Good Luck =)